1. Field of the Invention
The present invention relates to a drive signal generation circuit.
2. Description of the Related Art
A typical optical disc apparatus is provided with a sled motor for moving an optical pickup in a radial direction of an optical disc to read/write data from/to an optical disc such as CD (compact disc) (see, e.g., Japanese Patent Application Laid-Open Publication No. Hei7-045023 or 2003-153569.)
FIG. 7 depicts a typical sled motor control circuit 530 that drives a sled motor 520 for moving an optical pickup 500 in a radial direction of an optical disc 510. An RF amplifier 600 in the sled motor control circuit 530 outputs an RF (radio frequency) signal representing data recorded in the optical disc and a tracking error signal TE representing a tracking error based on a detection signal DET obtained by photoelectric conversion in the optical pickup 500. A defect detection circuit 610 compares a level of the input RF signal with a threshold value of a predetermined level to output a defect signal DEF indicating the presence of flaws, soil, etc., on the recording surface of the optical disc 510. A sled servo circuit 620 is a circuit that performs feedback control of the sled motor 520 so as to reduce the tracking error according to the input tracking error signal TE, and for which characteristics of a feedback loop for the feedback control of the sled motor 520 are set based on the level of the defect signal DEF (see. e.g., Japanese Patent Application Laid-Open Publication No. Hei7-045023.) Specifically, when the defect detection circuit 610 outputs the defect signal DEF indicating that no flaw, etc., exist on the recording surface of the optical disc 510, a coefficient is set for the sled servo circuit 620 so as to reduce the band of the feedback loop to reduce the power consumption of the sled servo circuit 620. On the other hand, when the defect detection circuit 610 outputs the defect signal DEF indicating that a flaw, etc., exist on the recording surface of the optical disc 510, a coefficient is set for the sled servo circuit 620 so as to increase the band of the feedback loop to accelerate the operation of the optical pickup 500. Therefore, the sled servo circuit 620 drives the sled motor 520 so as to reduce the tracking error based on the tracking error signal TE regardless of the presence of flaws, etc., on the recording surface of the optical disc 510.
The typical sled motor control circuit 530 performs feedback control of the sled motor 520 based on the tracking error signal TE. However, it is a problem that the accuracy of the tracking error signal TE input to the sled servo circuit 620 deteriorates in a period during which the defect signal DEF for indicating the presence of flaws, etc., on the recording surface of the optical disc 510 is output, and therefore, when performing the feedback control of the sled motor 520 based on the tracking error signal TE in this period, the optical pickup 500 is moved to a wrong position.